Drill string transmission circuit



May 18, 1965 R. H. KOLB ETAL DRILL STRING TRANSMISSION CIRCUIT Filed June 26, 1962 RECORDER FIG.

FIG. 2

FIG.3

INVENTORS:

R. H. KOLB T. R. REINHART WWZM THEIR ATTORNEY United States Patent 3,184,698 DRILL STRING TRANSMISSION CIRCUIT Robert H. Kolb and Tom R. Reinhart, Houston, Tex., assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed June 26, 1962, Ser. No. 205,409 3 Claims. (Cl. 339-16) This invention pertains to the drilling of boreholes, particularly oil wells, and more particularly a circuit for transmitting information from the bottom of the borehole to the surface during the drilling operations.

It is very desirable to transmit information from the bottom of the borehole to the surface during the drilling operations. Such information may indicate the inclination of the borehole or the character of the formations penetrated by the borehole. In the past, attempts to transmit information during the actual drilling operations have utilized various means, as for example pressure pulses in the circulating mud stream to telemeter information during drilling operations. Also, it has been suggested that radioactive elements or other marking devices could be released into the circulating mud stream to telemeter the information from the bottom of the borehole. These methods have limited accuracy and in the case of marking devices only a limited amount of information can be transmitted.

In addition to the above methods, it has also been suggested that the drill string plus the earth be used as an electrical circuit over which information could be telemetered. While this is possible, the drilling muds used are usually conductive and thus the signals will be shorted out between the drilling string and the surrounding earth formations. In an attempt to overcome these difficulties it has been suggested that an insulated electrical conductor could be disposed within the drill string and used along with the drill string as a transmission circuit. While electrical conductor have been suggested they have not been successful for various reasons, such as requiring additional time during the making up of the drill string. In addition, many of the previous devices were permanently installed in the drill string and could not be removed when no longer required. The use of permanent installations also required specially constructed drill strings and thus it was necessary to move the complete string from one drill site to the next.

Accordingly, the principal object of this invention is to provide a means for removably installing an electrical conductor within a standard drill string to provide a transmission circuit over which information may be telemetered during the drilling of an oil well or the like.

A further object of this invention is to provide a means for installing an electrical conductor in a standard drill string which requires no modification of the drill string and provides an automatic connection between the various segments of the conductors when the drill string is assembled.

A still further object of this invention is to provide a means for installing an electrical conductor within a standard drill string which may be installed in a drill pipe at a well site and easily removed when no longer needed.

A still further object of this invention is to provide a means for installing an electrical conductor within a standard drill string in which the coupling between the various segments of the conductor is by mechanical contact and requires no inductive or electr c-static coupling.

The above objects and advantages of this invention are achieved by providing a low impedance transmitter which is coupled to the cable of this invention. This cable consists of individual segments disposed centrally within the length of the individual sections of a standard drill string.

The individual connections between the various portions of the cable are in the form of mechanical contacts which have low contact resistance, thus minimizing the attenuation due to electrical leakage at each connection through the drilling mud that circulates through the drill string. Individual sections of the cable are provided with a male connection at one end and a spring-loaded female connection at the other end in order that the mechanical connection will be made automatically as the various sections of the drill string are assembled. Centralizing devices are provided for maintaining the cable centered within the drill string. In addition, the centralizing devices are provided with means for firmly gripping the cable in order that it may be held under sufiicient tension to maintain it centralized within the length of an individual section of the drill string. Finally, the centralizers are provided with outwardly extending peripheral flanges which engage existing shoulders on the individual sections of a standard drill string. The electrical circuit is completed by the use of the drill string as the second conductor.

The above objects and advantages of this invention may be more easily understood from the following detailed description of a preferred embodiment when taken in conjunction with the attached drawings in which:

FIGURE 1 is a schematic view of a drill string showing the use of the cable of this invention to telemeter information from the bottom of the borehole to the surface;

FIGURE 2 is an enlarged section of a portion of the drill string showing the construction details for mounting cable within the drill string; and,

FIGURE 3 is an end view of one of the devices used for centralizing the cable within the drill string.

Referring now to FIGURE 1, there is shown a borehole 10 having a drill string 11 disposed therein. Disposed adjacent the lower end of the drill string is an instrument housing 12 that measures a characteristic of the formation for the borehole that is desired. The instrument housing may take various forms as for example it may be an inclinometer which measures the inclination of the borehole during the course of drilling, or it may be an instrument for measuring the resistivity of the formation or other characteristics of the formation. Similarly, the instrument housing may measure such things as the wear of the drilling bit as it penetrates the formations. The signal source or instrument 12 must be of low impedance and supply a low frequency or pulsed signal. This signal may be coupled to the conductor 13 disposed Within the drill string 11, as for example by inductive or direct means. In the case of inductive coupling the primary may be formed by a toroidal coil and the conductor 13 in the drill string 11 may form the secondary. The conductor 13 as will be explained below is a low-impedance circuit to reduce the attenuation caused by leakage at the various joints. This also reduces the leakage at sections of the cable that are damaged during the handling thereof. The signal transmitted over the cable 13 is removed at the surface through a normal slip ring arrangement, inductive means or short range radio transmitter receiver. The signal once removed may then be recorded by means of a recorder or utilized to control the drilling operation or for other purposes.

Referring now to FIGURE 2, the details of the conductor 13 and its installation Within the drill string 11 are shown. The conductor 13 is preferably a large solid conductor 14 having a heavy insulation 15 for example, the conductor 14 may be formed from a composite material having a steel inner core surrounded by a copper shell. This construction results in a conductor having high mechanical strength while still maintaining a reasonably low electrical resistance for transmitting electrical energy. The upper end of the conductor 13 is held in the center of the drill string 11 by means of a centralizing member 16. The centralizing member as shown in FIG- URE 3 is preferably formed of a molded plastic material having an outer ring 21 and a central section 22 supported by two webs 23. The centralizing member 16 should also be of minimum cross section consistent with the required strength and streamlined to minimize the interference with the mud flow through the drill string. The outer ring 21 is provided with an outwardly extending shoulder 24 that engages a sloping shoulder 25 formed on the end of the drill string 11. As seen in FIGURE 2, the shoulder 25 is formed at the end of the internal thread 18 that is used for coupling the various sections of the drill string together and is present in all standard drill strings. The insulation is removed from the end of the conductor that passes through an opening formed in the central section 22 in order that this end of the conductor may form the male connector of the conductor. The conductor is held in the center opening 22 by means of a sleeve 26 which is pressed into the center opening 22 and tightly engages the conductor.

The lower end of the conductor 13 is supported by a centralizing member 30 which is similar in construction to the centralizing member 16 described above. The centralizing member 38 is also formed from a molded plastic material. An annular member 31 formed from metal and having a Z shaped cross section is positioned in the end of the drill string. One flange 32 of the member 31 engages the end 33 of the drill string 11. The end of the centralizing member 30 engages the inwardly projecting flange 34 of the member 31. The lower end of the conductor 14 is coupled to a spring-loaded female connector 35 by any desired means not shown in FIG- URE 2. For example, the conductor may be coupled to the female connector by various means such as crimping or other locking means. The conductor is held in the centralizing member 30 by means of a locking device 36 disposed at the inner end of the centralizing member 39. The locking member securely locks the conductor to the centralizing member by means of a heavy mechanical crimp or the like.

When the above-described conductor arrangement is to be installed in a drill string the centralizing members 39 are first attached to one end of a length of conductor 13. Of course, the length of conductor 13 should be of sufiicient length to extend through the section of the drill string. While the conductors must be of the proper length it is not necessary that they be the exact length of a section of drill string since after connections are formed the excess conductor is cut off. Once the con ductor is attached to the centralizing member 3!) it is passed through the section of the drill string and the other centralizing member 16 positioned over the end. As explained above, before the centralizing member 16 is attached to the conductor the insulation is removed from a portion of the conductor to form the male fitting. Next the conductor is placed under tension as by means of a jacking device attached to the bare, upper end of the connector and the locking sleeve installed and secured by crimping. By maintaining the conductor in a taut condition, the conductor will be disposed in the center of the drill string and any tendency of the conductor to whip during the rotation of the drill string will be greatly reduced. Suitable devices for connectors 26 and 36 are Thomas and Betts Part No. 8L100 wedge-on terminals. After a conductor is installed within each section of the drill string the drill string may be assembled in the normal manner and the individual sections of the conductor will automatically be connected by means of the male and female connections. This connection is accomplished without any further attention on the part of the personnel that are assembling the drill string. Likewise, the conductor is installed completely within the drill string 11 and thus it will not be subject to mechanical damage as the drill string is pulled from the well and disassembled and placed in the drilling derrick.

As explained above, it is preferable to use a low-impedance signal source that may be coupled to the conductor of this invention by various means. The individual sections of the conductor have a relatively low impedance, thus the losses due to electrical leakage through the connections will be relatively small. Accordingly, it is possible to readily transmit a signal from the bottom of the drill string to the surface without further need of amplifiers or repeaters. Of course, when very deep wells are to be drilled, or under adverse conditions, it may be necessary to include repeating devices within the drill string to amplify the signals as they are transmitted over the conductor.

The low-impedance conductor establishes a preferential path for the electric current to flow. By having the cable impedance low with respect to a leak due to bare wire or a damaged section of insulation, a major portion of the current will take the path of least resistance and continue down the cable while only a small amount will be lost through the leak. Thus a signal of suificient strength will reach the surface. It is, of course, appreciated that while the system of this invention is designed to operate with some electrical leaks, steps are taken to minimize the number of such leaks. As for example, the connections between various sections of the cable are insulated to substantially prevent leakage. These features also result in a very economical conductor installation that may be discarded when no longer needed.

We claim as our invention:

1. A transmission cable for a drill string comprising:

a drill string formed from a plurality of sections;

a single conductor disposed in the center of each section of the drill string, said conductor having a male fitting disposed adjacent one end of each section and a spring-loaded female connector disposed adjacent the other end of each section; and

a removable centralizing means disposed in each end of each section, one of said centralizing means in each section fixedly retaining the male fitting and the other of said centralizing means in each section fixedly retaining the female connector of the conductor within the section in which the centralizer is mounted, said pair of centralizing means in each section of said drill string engaging the respective ends of the section to maintain said conductor under tension and substantially centralized within each section.

2. A transmission cable for a drill string formed from a plurality of sections, each of said sections including:

a single insulated conductor disposed in the center of said section of the drill string, one end of said conductor having its insulation removed to form a male connector; the other end of said conductor being joined to a female connector;

a first centralizing member, said first centralizing member engaging and retaining the male connector of said conductor, the outer peripheral surface of said first centralizing member engaging an inwardly extending shoulder formed on said section of the drill string at one end thereof;

a second centralizing member, said second centralizing member engaging and retaining the female connector of said conductor; and

an annular member having an outwardly projecting flange at one end and an inwardly projecting flange at the other end, said annular member being positioned in the other end of said section of the drill string with said outwardly projecting flange engaging said other end of the section, said second centralizing member engaging the inwardly projecting flange of said annular member to maintain said conductor under tension; whereby the respective male and female connectors in adjacent sections of the drill .5 string are coupled to form a continuous transmission cable when the drill string is assembled.

3. In a transmission cable for a multi-section drill string:

a section of drill string;

a centralizing member disposed in each end of said section of drill string, said centralizing members being restrained to prevent axial movement toward the center of said section of drill string while permitting the removal of the centralizing member from said section of the drill string;

a single insulated conductor disposed in the center of said section of drill string and extending to the centralizing members on opposite ends of said section, one end of said conductor having the insulation removed to form a male connector, said one end being secured to one of said centralizing members with said male connector projecting beyond said centralizing member, the other end of said conductor being secured to a female connector, said female 20 connector being connected to the centralizing memher at the other end of said section of drill string to maintain said conductor under tension within said section; whereby sad female connector will receive a male connector in an adjacent section to form a continuous transmission cable when the drill string is assembled.

References ited by the Examiner UNITED STATES PATENTS 2,615,949 10/52 Hecking 174-88 2,748,358 5/56 Johnston 174-47 X 2,750,569 6/56 Moon 174-47 3,040,288 6/62 Edlen et al. 174-75 3,041,875 7/62 Reesby 339-16 X JOHN F. BURNS, Primary Examiner.

JOHN P. WILDMAN, Examinef. 

1. A TRANSMISSION CABLE FOR A DRILL STRING COMPRISING: A DRILL STRING FORMED FROM A PLURALITY OF SECTIONS; A SINGLE CONDUCTOR DISPOSED IN THE CENTER OF EACH SECTION OF THE DRILL STRING, SAID CONDUCTOR HAVING A MALE FITTING DISPOSED ADJACENT ONE END OF EACH SECTION AND A SPRING-LOADED FEMALE CONNECTORE DISPOSED ADJACENT THE OTHER END OF SAID SECTION; AND A REMOVABLE CENTRALIZING MEANS DISPOSED IN EACH END OF EACH SECTION, ONE OF SAID CENTRALIZING MEANS IN EACH SECTION FIXEDLY RETAINING THE MALE FITTING AND THE OTHER OF SAID CENTRALIZING MEANS IN EACH SECTION FIXEDLY RETAINING THE FEMALE CONENCTOR OF THE CONDUCTOR WITHIN THE SECTION IN WHICH THE CENTRALIZER IS MOUNTED, SAID PAIR OF CENTRALIZING MEANS IN EACH SECTION OF SAID DRILL STRING ENGAGING THE RESPECTIVE ENDS OF THE SECTION TO MAINTAIN SAID CONDUCTOR UNDER TENSION AND SUBSTANTIALLY CENTRALIZED WITHIN EACH SECTION. 